1. Field of the Invention
The present invention generally relates to a method of plasma etching, and more particularly to a method of plasma etching improved to enhance its anisotropic property. The present invention further relates to apparatus for implementing such a plasma etching method.
2. Description of the Prior Art
In manufacturing dynamic random access memories of 4-megabits or even higher integrated devices, the use of pattern of submicron is indispensable. It is necessary to form pattern having anisotropic profile without contamination and damage to implement submicron pattern for manufacturing VLSI devices. As technology satisfying this demand, a new etching technology using electron cyclotron resonance (hereinafter referred to as ECR) is proposed (1988 DRY PROCESS SYMPOSIUM p.9).
The plasma etching using ECR (hereinafter referred to as ECR plasma etching) is employed to perform etching of metal used for single crystal silicon, polysilicon, interconnection or the like with plasma of halogen gas such as C.sub.l2 gas or the like. This method enables etching of a substrate to be treated without contamination and damage.
FIG. 5 is a sectional view of a conventional plasma reaction apparatus employing ECR. The plasma reaction apparatus has a sample chamber 2 for accommodating a substrate 4 to be treated. A sample shelf 3 on which the substrate to be treated 4 is carried is provided in sample chamber 2. A plasma producing chamber 1 for producing plasma in it is connected to the upper part of sample chamber 2. A microwave introducing opening 5 is provided in the upper part of plasma producing chamber 1. A microwave source 6 is connected to microwave introducing opening 5 by a waveguide 40. Microwave source 6 is, for example, a magnetron or a klystron. Magnetic coils 9a, 9b for producing a magnetic field in plasma producing chamber 1 gas provided around plasma producing chamber 1. A gas introducing opening 50 for introducing reactive gas or the like into plasma producing chamber 1 is provided in the upper part of plasma producing chamber 1. An exhaust port 8 for exhausting the gas inside sample chamber 2 is provided in the lower portion of sample chamber 2.
Next, operation of the plasma reaction apparatus will be described. FIGS. 6A and 6B are sectional views showing the process of etching a substrate to be treated employing the plasma reaction apparatus.
The substrate 4 to be treated located on sample shelf 3. Referring to FIG. 6A, the substrate 4 is made by forming an oxide film 55 on a semiconductor substrate 53, forming an aluminum alloy film 54 on oxide film 55, and forming a resist pattern 52 with a predetermined form on the aluminum alloy film 54. Next, while introducing reactive gas (C.sub.l2, Br.sub.2 or the like) into plasma producing chamber 1 through gas introducing opening 50, gas is exhausted through exhausting port 8. By this operation, the inside portion of plasma producing chamber 1 and sample chamber 2 is maintained at a predetermined degree of vacuum. In this condition, a magnetic field is produced in plasma producing chamber 1 by means of magnetic coils 9a, 9b. The microwave is supplied to plasma producing chamber 1 through microwave guide 40 from microwave source 6. The strength of the magnetic field is 875 gauss, for example, the frequency of the microwave is 2.45 GHz. Thus, electrons in the reactive gas absorb energy from the microwave and moves spirally. The spirally moving electrons impact against the reactive gas molecules, high density plasma of the reaction gas is produced thereby, and a plasma region 20 is produced in plasma producing chamber 1. The plasma of the reactive gas produced in plasma producing chamber 1 is transported into sample chamber 2 by magnetic lines of force. The gas plasma of the reaction gas transported into sample chamber 2 etches the surface of the treated substrate 4.
The surface etching of substrate 4 will be described in detail referring to FIG. 3B.
FIG. 3B shows the motion of the reactive ion species in a conventional plasma etching method. C.sub.l2 gas is used as the reactive gas. Referring to FIG. 3B, a substrate 4, which is to be treated, is carried on a sample shelf 3. Substrate 4 includes semiconductor substrate 53, an oxide film 55 formed on the semiconductor substrate 53, an aluminum alloy film 54 formed on the oxide film 55 (etched to be an interconnection), and a resist pattern 52 formed on the aluminum alloy film 54.
Now, when a plasma region 20 is formed a sample chamber (not shown in FIG. 3B), the sample shelf carrying the substrate 4 which is to be treated is negatively charged. Then, a strong electric field region referred to as a sheath region 51 is produced between plasma region 20 and sample shelf 3. The reactive ions (C.sub.l.sup.+) in plasma region 20 are accelerated by means of the electric field in the sheath region 51 and directed onto substrate 4. In this way, aluminum alloy film 54 is gradually etched, as shown in FIG. 6B , to give an interconnection pattern 54a. According to this method, the etching of aluminum alloy film 54 can be performed without contamination and damage of the substrate to be treated 4 under treatment.
However, as a feature of the ECR discharge, because of the weak electric field of sheath region 51, as shown in FIG. 3B, the reactive ions (C.sub.l.sup.+) existing in plasma region 20 do not vertically impinge onto the substrate 4 being treated. Thus, in the ECR discharge, sufficient anisotropic etching can not be performed, and referring to FIG. 6B, the sectional shape of interconnection pattern 54a becomes taper-like.
As another prior art in connection with the present invention, Japanese Patent Laying-Open No. 60-217634 discloses a plasma etching method, although it is not a method using the ECR discharge, characterized by plasma etching aluminum or the like a mixed gas including chlorine type reactive gas and hydrogen gas. However, since the ECR discharge is not employed in this method, they have had problems such as contamination and damage of a semiconductor substrate. Also, in this prior art, H.sub.2 gas only is disclosed and no disclosure was made with respect to other gases with which the anisotropic property seems to be enhanced.